It is a basic need for workmen working with telephone or other communications cables to be able to communicate with other workmen who are working with the same cable. In conducting certain types of tests in which a sequence of steps is required, constant communication between workmen is a must. Also when cables are being placed, communication between workmen is a necessity. Such communication is not a serious problem so long as access to a cable with metallic conductors is available. If metallic conductors are available, a workman merely connects a headset and a battery to an unused cable pair on one end, and is able to talk to a workman on the other end who has only a headset.
However, a serious problem does arise when access to metallic conductors is not available. This commonly occurs when the cable is being placed and has not yet been opened by the workmen. Another case is that in which non-metallic cables are used, such as fiber optic cables. In these two cases, the workman has had no choice but to open a metallic cable in order to establish a communications link, or to use a more exotic communications link such as radio or fiber optic links. Radio works fairly well but is limited in range, particularly when one or both of the workmen are in underground locations or inside buildings. On fiber optic cables a fiber optic talk set can be used, but the equipment required is expensive and will only work if the cable is open and a termination point is available.
It is thus apparent that there is a need tor a new method of communicating over unopened metallic cables and fiber optic cables, which method involves easy set up; is inexpensive; is reliable up to a distance of several miles and does not require either the opening of a cable or a termination point. It is accordingly the objective of this invention to provide such a new method.